Looms for weaving terry cloth require gear drives that are capable of driving two different motion sequences, since it is necessary to position the slay shaft at different angular orientations for the formation of the terry loops or nap. For example, one orientation of the slay shaft must enable the formation of a partial beat-up for forming the pile depth of the warp threads for the terry cloth being woven, while the other angular position of the slay shaft must enable the full beat-up motion of the reed.
European Patent Publication EP-0,350,446 (Spiller et al.), published Jan. 10, 1990, describes a method and a loom for weaving terry cloth with features for the terry pile or nap formation. In the known loom the several angular positions of the slay shaft and thus of the reed are achieved in accordance with the principle of a so-called toggle slay comprising a plurality of articulated toggle levers. One of these articulated toggle levers bears against an eccentric cam assembly which is rigidly coupled to the main drive shaft of the loom. The toggle levers influence the angular position of the reed relative to a cam follower lever also referred to herein as roller carrying lever or simply as cam follower. The toggle lever is connected to a respective adjustment drive for varying or adjusting the position of the toggle lever, whereby the just described features of the known apparatus make it possible to adjust the toggle lever translation ratio of the toggle slay in the direction of the reed or rather relative to the beat-up line.
In connection with the use of a gear drive which cooperates with a toggle slay, there is the drawback that the kinematic system altogether is inherently "soft". In the present context the term "soft" means that the position of the pivots or journal axis of the system cannot always be exactly reproduced to assume the same position at all times. This drawback of a toggle slay leads to a certain inaccurate beat-up motion of the slay for the formation of the terry pile or nap. The adjustment drive of the known slay drive system has a spindle for the adjustment and positioning. Nevertheless, such a spindle drive has the disadvantage that it is not compatible with the high r.p.m. of the main loom drive shaft because a rapid sequence of adjustment motions is necessary and such motions have their speed limitation when a toggle slay is used.
Furthermore, the use of a plurality of interacting toggle levers has the disadvantage of a substantial inertia which also militates against the use of a high speed drive shaft r.p.m. The inertia of the toggle lever system also has an adverse influence on the wear and tear resistance of the bearings in the entire system.